1. Field of the Invention
This invention relates generally to means for automatically releasing a jack support member for lowering the same, and more particularly to an automatic release mechanism operable with a two-part jack system having a jack stand and a power unit.
2. Description of the Related Art
The two part jacking system in which the present invention is best used is best described in U.S. Pat. Nos. 4,462,569 and 4,589,630.
Briefly, the two part jacking system consists of a power unit and a set of separate mechanical jack stands. The stands are capable of being vertically extended and retracted and, when extended, can be locked in place at any desired position by a ratchet and pawl assembly. The chassis of the power unit is adapted to mate with and carry the jack stands for placement or removal.
In use, the power unit is operated entirely from its handle. It is maneuvered under a vehicle to place the jack stand in the desired location for lifting and supporting the vehicle. The power unit, activated from the handle, then vertically extends this jack stand to the desired height thus lifting the vehicle on the stand. By operating the controls at the end of the handle, the operator can cause the power unit to disengage from the stand, which will remain locked in its extended supporting position under the vehicle. In this manner, the vehicle is raised and supported on a separate mechanical stand without transferring the vehicle from a jack to a stand and without the operator placing any part of his body under the vehicle or having to touch the stand itself. After the stand is raised and locked in place to support the vehicle or other load in a lifted position, the power unit lift arm is lowered and the power unit is disengaged from the stand and pulled away, leaving the stand in position supporting the load.
To lower the vehicle and remove the stand, the power unit is maneuvered to re-engage with the stand. By manually operating a control at the end of the handle, the user can cause the power unit to re-engage with the stand, disengage the ratchet locking system of the stand and lower the stand to its original position. The power unit remains engaged with the stand and can be pulled away from the vehicle with the stand carried in its chassis.
This prior art system however, requires manual intervention by the user to disengage the ratchet locking system of the stand at the proper moment when the loading forces on the stand are transferred to the lifting arm of the power unit. As the stand is remote from the user, the determination of the proper timing to disengage the ratchet locking system is difficult and may, in some instances, force the user to place himself under the vehicle or to touch the stand to determine when the loading forces are removed from the stand by action of the lifting arms of the power unit. This situation obviates the safety features of the two part jacking system and subjects the user to the possibility of a serious accident.
The present invention overcomes this prior art problem by providing a mechanism for automatically releasing the stand when the loading forces on the stand are removed by the lifting arms of the power unit. Thus, the safety features of the two-part jack system that permit the raising and lowering of a vehicle or other load without a user having to place any part of his body under the vehicle or other load, are preserved.